The invention relates to a pump arrangement, in particular magnetic clutch pump arrangement.
The pump arrangement has an interior space formed by a pump casing, a containment can which has a central longitudinal axis and which hermetically seals off a chamber surrounded by said containment can with respect to the interior space formed by the pump casing, an impeller shaft which can be driven in rotation about an axis of rotation, an impeller which is arranged on one end of the impeller shaft, having an inner rotor arranged on the other end of the impeller shaft, and an outer rotor which is arranged on a drive shaft and which interacts with the inner rotor. The containment can has a base with at least one bead which projects into the chamber. The invention also relates to a method for producing a containment can of a pump arrangement.
In the case of such pumps, the rotating magnetic field induces eddy currents in the metallic containment can situated between inner rotor and outer rotor. Said statically positioned containment can, together with the casing cover and the pump casing itself, forms the pressure-bearing pump part, whereby the inner rotor, which is situated within said enclosure, is in constant contact with the delivery medium. To reduce the eddy currents and the associated continuous heating of the medium to the point of evaporation, use is firstly normally made of metallic containment can materials with high electrical resistance. Particularly expensive nickel-based alloys (Hastelloy) have become established for this purpose. Secondly, the heat losses are dissipated by way of a cooling flow. Said flow, which is branched off as a bypass from the main delivery flow, is, owing to the pressure distribution in the chamber, transported over the outer diameter of the inner rotor, in a radially inward direction between inner rotor and containment can base to the impeller shaft, and back to the main hydraulic system via a hollow bore in said impeller shaft. Owing to the rotation of the inner rotor and the resulting formation of vortices in the bypass flow of the delivery medium, an excessive pressure gradient arises between the inner rotor outer diameter and the inlet, situated coaxially with respect to the axis of rotation, of the hollow bore of the impeller shaft. The cooling flow rate and thus the heat dissipation are restricted. Integration of a geometry, which has the effect of impeding or breaking up vortices in the delivery medium, on the static containment can base can prevent or limit this, whereby the inertial rotor chamber temperature remains at a corresponding level below the vapor pressure curve of the delivery medium.
German patent document no. DE 91 00 515 U1 has disclosed a magnetic coupling pump in which it is intended to reduce the formation of swirl phenomena in the delivery medium by way of a bead provided in the base of the containment can. The pressure loading-optimized geometry or shape of the base without beads results from the expandability or deformability of the convex-ellipsoidal base under load. This is however impeded owing to the centrally provided beads, which thus have a stiffening action. This results in increased stresses in the containment can material of the bead region. In relation to convex-ellipsoidal shapes without beads, and using the same wall thicknesses or starting material thicknesses, the disclosed bead contour achieves a compressive strength of only approximately 40%. In this way, an equal compressive strength can be attained only through the use of more material, with an associated increase in costs.
It is the object of the invention to provide a pump arrangement in which the formation of vortices in the delivery medium within the containment can is further reduced, without reducing the stability of the containment can.
The object of the invention is achieved in that the at least one bead is arranged with a radial spacing to the central longitudinal axis of the containment can, wherein the ratio of inner radius of the containment can to spacing of bead outer edge and central longitudinal axis of the containment can lies in a range from 1.3 to 1.6.
The ratio of inner radius of the containment can to spacing of bead outer edge and central longitudinal axis of the containment can preferably lies in a range from 1.38 to 1.57.
The spacing of the bead inner edge to the central longitudinal axis of the containment can is advantageously 1/7*containment can inner radiusY, wherein Y preferably lies in a range from approximately 1.14 to 1.17.
Through such a specification of the ratio of inner radius of the containment can to radius of the bead outer edge, or of the spacing of the bead inner edge to the central longitudinal axis, the axial expandability or deformability of the containment can base is maintained, whereby the pressure-withstanding capability is maintained to a degree of 90 to 95% in relation to a containment can base of the same wall thickness without beads.
In a preferred implementation of the invention, for a high compressive strength of the preferably deep-drawn or cast containment can, the base thereof is formed by a substantially spherical—segment-shaped spherical cap region and by a rim region which forms the transition region between main body and spherical cap region.
According to the invention, for an optimum spacing between inner rotor and the bead base, the bead base runs in a plane which is situated substantially parallel to the plane in which the transition from the spherical cap region to the rim region is situated. The imaginary planes lie substantially perpendicular to a central longitudinal axis of the containment can.
Here, in a particular refinement, it is provided that the inner wall of the containment can in the region of the bead base lies substantially in the same plane as the transition from the spherical cap region to the rim region.
In an alternative refinement, the bead base is formed so as to run parallel to the spherical cap region.
A good mode of operation with regard to the reduction of vortex formation is achieved if, in the region of the bead base, the maximum spacing of the inner wall of the containment can to the face side, facing toward the base of the containment can, of the inner rotor is approximately 20 mm.
It is preferable if, in the region of the bead base, the maximum spacing of the inner wall of the containment can to the face side of the inner rotor is approximately 10 mm, in order to further reduce vortex formation.
Since the mechanical stresses are at their greatest at the transition from the spherical cap region to the bead region, and sharp-edged transitions are the most effective for preventing the formation of vortices, it is provided according to the invention that the transitions between the spherical cap region and the bead walls have greater radii than the transitions from the bead walls to the respective bead base. At the same time, it is possible for the pressure acting outwardly in the chamber enclosed by the containment can to be accommodated in a particularly effective, that is to say low-stress manner.
If the at least one bead extends in a radial direction to a point close to the rim region, or extends as far as the latter, the vortices that arise in the chamber enclosed by the containment can (said vortices being most pronounced at the inner rotor in a region with the greatest circumferential speed, that is to say close to the outer diameter of the rotating inner rotor) are effectively reduced.
A method according to the invention provides that the containment can is produced by way of a deep-drawing process or by way of a casting process, wherein at least one bead is produced in the base, which bead is arranged with a radial spacing to the central longitudinal axis of the containment can.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.